The present invention relates generally to single bit failures of integrated circuit memory devices, and more specifically to a circuitry and methodology to test single bit failures of integrated circuit memory devices.
Testing is performed throughout the manufacture and assembly of integrated circuit memory devices in order to ascertain their functionality and reliability. Testing of internal cell electrical measurements of integrated circuit memory devices is becoming more and more useful in determining the root cause of single bit failures of memory devices. Single bit failures may be caused by a variety of conditions, including intrinsic process or design problems such as a contact overetch condition, particle defects, shorts in circuitry, and mechanical damage to circuits such as photolithic defects.
The traditional method of internal cell electrical measurement in order to test single bits of an integrated circuit memory device is performed by first choosing a certain cell to be analyzed by some type of functional test. Next, Focused Ion Beam (FIB) and/or laser modifications are typically made to access and disconnect the cell to be tested from its associated loads and other circuitry which might otherwise taint the internal cell electrical measurements. FIB technology may be used to make contact to bitlines of an integrated circuit memory device, disconnecting column loads and measuring I-V (current-voltage) characteristics of the memory device while modulating FIB bitline pads. FIB technology may also be used to cut metal lines of the integrated circuit memory device or to deposit metal to reconnect broken metal lines or to construct a pad which may be probed on a die. Finally, tedious and time consuming internal microprobing of the cell is necessary to make actual measurements.
Since internal cell electrical measurement of single bit failures is currently performed manually and is thus very labor intensive, a test mode feature of an integrated circuit memory device which analyzes single bit failures would be very useful in the art.